Knowledge-based company of Hoorpendar, as the first designer and manufacturer of static excitation system of power plant generator, is ready to design, produce and provide the services required by its customers in the field of generator excitation system. SECON-2000 series excitation system includes static excitation systems up to 2000A single power or with plug.

  • PLC-based digital controller
  • Voltage regulation with accuracy ± 0.5%
  • Fast performance response
  • Multiple excitation limiter to keep the machine in the allowable operating range
  • Six thyristor rectifier bridge 12 full pulse
  • Input contactor or Circuit Breaker switch (optional motorized) in the input power supply
  • Crowbar & Field Discharge
  • DC field switch (optional)
  • Field Flashing control circuit and driver using IGBT technology
  • High power indoor air supply system
  • LCD screen with touch screen to display values and control locally or remotely
  • Digital communication with modern facilities
  • Overload bearing capacity for a short time
  • Overvoltage protection of the field
  • Reliable stability in operation with the network or other machines
  • Generating thyristor trigger pulses even in the event of possible errors
  • Provide excitation current up to 2000A
  • Ability to create Redundancy for control and thyristor bridges
  • Compatible with most power plant control systems
  • Ability to detect and view errors remotely

Voltage Regulation

SECON-Digital regulates RMS generator voltage from idle to full load with an accuracy of ± 0.5%, digital signal processing and efficient regulation algorithms are the result of Horpandar’s experience and expertise in designing and implementing control systems. Using advanced hardware, the French company Schneider has provided a reliable and stable system.

Out put

SECON-Digital provides an isolated 4-20mA or 0-10Vdc isolated analog output signal for the power supply angle control circuit. The DC current generated by the power supply provides the current of the generator field or excitation. SECON-Digital can actually support any other rectifier bridge that can be controlled with this analog signal, which can be a advantage for many synchronous motors or generators with faulty controllers. Be efficient.

Stability

SECON-Digital uses a stable PID controller (Proportional, Integral, Derivative). SECON-Digital has a stable stable initialized programming (PID). Therefore, a stable standard setting is considered for most machines. In addition, in SECON-Digital it is possible to fine-tune the parameters with a group of other settings according to each generator to optimize the system performance. The settings software includes a PID selection program that helps select the correct PID.

SECON-Digital also includes minimum and maximum excitation limits, VAR / PF controllers and stator current limiter to optimize stability and performance in transient conditions. Additional stability parameters are considered.

PID settings (PID)

SECON-Digital has made it possible to reset the PID parameters precisely to optimize system stability for different machines. The software is smart in this area and prevents numbers from entering outside the allowed range.

Under frequency limiter or V to Hz ratio (Under frequency limiter or V / Hz Ratio limiter)

SECON-Digital offers the customer two choices: sub-frequency limiter or V / Hz ratio limiter. This limit prevents the generator from overflowing..

(Soft-Start Voltage build-up)

SECON-Digital has a soft voltage controller whose parameters can be adjusted by the user. This soft starter controls the allowable rate of increase of the generator voltage and prevents over-jump of the voltage during start-up of the generator. Soft startup is enabled in both AVR and FCR modes.

Set point Control

SECON-Digital allows the work point to be set remotely in addition to the local panel. The operating mode operating point can be set from Raise / Lower contacts or analog input signal 4-20mA or ± 10Vdc. These settings are also available through communication ports according to the Modbus protocol.

Field Current Regulation operating Mode

SECON-Digital provides a manual operation channel called field flow regulation mode (FCR). In this mode, SECON-Digital regulates the output current of the power bridge. This mode is not dependent on the generator voltage measurement input and thus provides a backup to control the excitation when the voltage input is lost. In FCR mode, the operator must manually adjust the excitation current to achieve the rated voltage based on load changes.

VAR or PF control function mode

(VAR / Power Factor Controller Operating Mode)

SECON-digital also has two additional control modes for using the generator when connecting to the global network. In VAR control mode, SECON-Digital can regulate the amount of reactive power of the generator output to the set value required by the operator, or in PF mode it can control the amount of reactive power of the generator output according to the active power changes. Regulate the required limit

 

Summing Point Type OEL

In this method, three levels of high-medium-low OEL current are defined for on-line operation. To act. Two levels of high and low OEL current are defined for off-line operation (main key open). The generator can operate continuously at low OEL current level and for programmed time at high OEL current level.

Take Over Type OEL Control Overdrive The Over Over method determines a field current level whose range is in an inverted time profile. Two adjustments of flow levels and time components are defined for the Take Over method. Separate curves may be selected for On-line and Off-line operation. If the system enters the above excitation conditions, the excitation current is limited by following a selected curve. The selection of on-line and off-line surfaces and curves is achieved by a selective OEL.

Minimum Excitation on Limiter

The minimum excitation limiter prevents the reduction of the generator field current below the safe operating level. This restriction prevents the poles from slipping and damaging the machine. This also limits the amount of reactive power absorbed by the machine based on the operator-defined settings. A minimum excitation limit curve (UEL) based on an allowable reactive power level at zero active power can be used for this purpose.

The UEL limiting function is optional in FCR mode.

Stator Current Limiter

Stator current limiter (SCL) measures the stator current and prevents the stator temperature from rising. The SCL limiter operates in all modes except the FCR operation mode.

In FCR mode, the controller announces the stator overcurrent conditions but the limiter is off. There are two levels of SCL flow: high and low. The generator can operate continuously at the SCL current level but at the SCL high current level only for a scheduled time.

Auto tracking between operating modes

SECON-Digital is a smart device that can automatically change the setting point by changing the control modes. This allows the operator to change the control mode during operation without causing a bump (Lump) so as not to disturb the power system..

Replacement of old controllers with the modern digital system of static excitation SECON-2000 designed according to the customer’s order. A number of power plants in the country have outdated equipment, with high repair costs and the impossibility of providing spare parts. DC cut-off switches, motorized rheostats, faulty rotating actuators, damaged commutators, wear and tear of various components in voltage regulators are just some of the problems of the country’s old power plants, which results in increased overhead costs and increased generator downtime.

Replacing rotating compound stimuli or SCT / PPT controls with a SECON-2000 series excitation stimulation system is a viable solution to these problems.

SECON-2000 digital static excitation with flexible design has made it possible to update the old systems of the country’s power plants with economic justification and can be used for most small and large power plants in the country.

  • The coil of the swivel excitation system is short-circuited or partially discharged.
  • To increase the range of the generator, you need to increase the excitation current.
  • Increased repairs and downtime have reduced system reliability.
  • The carbon dust from the commutator brush reduces the insulation and raises the temperature.
  • Due to the carbon dust in the commutator, problems such as spark or reduced insulation have been created.
  • Your generator commutator is worn out and needs to be replaced.
  • The vacuum cleaners of the commutators need to be repaired regularly and their overhaul is also difficult.
  • It is not possible to supply spare parts for existing electromechanical equipment.
  • The DC field switch is difficult to operate and its replacement is very costly and time consuming.
  • You need an automated excitation system in your control unit for automatic start-up or automatic synchronization.
  • You need a system with a fast voltage compensator to be compatible with the new relays and to prevent unwanted trips.
  • You want to increase your performance efficiency by increasing the unit output excitation by reducing consumption.
  • You do not have enough repairmen to repair electromechanical and rotating parts.
  • You need the ability to record information, and this feature is present in digital excitation systems.

The basic principles of a static excitation regulator are continuous measurement of voltage and current and comparison with adjustment points and application of new voltage suitable for excitation. When the excitation system senses a decrease in generator voltage, it increases the field current, and when it senses an increase in generator voltage, it decreases the excitation current. In this case, DC static excitation is applied directly to the field through the Slip Ring.

A normally designed static excitation system may have several different parts, but there are always six basic components at the core of the system.

The main components are:

  • Digital AVR
  • Power Electronics Thyristor Bridge))
  • Measuring Instrument)
  • SCR Firing Unit))
  • Touch Screen HMI and Switches
  • Main power supply Shunt Transformer or PMG))

In the custom design of the excitation system, various capabilities and facilities can be selected for your application. Suggested features include:

  • Redundancy of the Power Electronics))
  • Redundancy of the Control Electronics)
  • Several digital connections to different protocols
  • Digital generator protection relays
  • Remote control and integration with DCS control system and turbine control panel
  • Field Flashing system
  • Fast De-excitation system
  • Automatic synchronizer
  • Coordinate with available space and boards

The heart of the SECON-2000 excitation system is its digital controller. This part has been selected by a programmable controller (PLC) from Schneider Premium series. This PLC, which is of industrial type, receives the values of various parameters that are read by the measuring equipment and is in the standard range of voltage or current through its analog input cards and the status and error signals of the system through its digital input cards. After analysis and processing in its powerful processor section, it applies digital commands through the digital output card and the amount of voltage required for the rectifier bridge in the form of analog values through the analog output card.

The digital controller, while providing the analog signal of the fire pulse section and controlling the DC voltage of the thyristor bridge rectifier output, continuously monitors the system to control, apply the limitations and the operation of the synchronous machine within its tolerable range.

Real Time monitoring for testing and analysis, graphical display of parameters, display of digital input and output statuses are other features of this section that can be accessed by software provided for PC.

The specifications of this section are as follows:

  • PLC based design
    It has four control modes with the ability to change the working mode without creating a shock
  • Automatic Voltage Regulation (AVR)
  • Field Current Regulation (FCR)
  • Power Factor Regulation (PFR)
  • Var control
  • 0.5% accuracy of voltage regulation
  • Two programmable analog outputs for analog display
  • Perform settings by computer software or HMI
  • PID controller
  • Line voltage drop compensator
  • Soft voltage starter made initially
  • Flexible remote control points
  • Implemented limiting functions
  • Above stimulation limiter
  • Restrictor following stimulation
  • Volts / HZ ratio limiter or frequency reduction limiter
  • Stator current limiter
  • Input contact
  • Relative analog voltage or current
  • Digital communication
  • Implemented protection functions
  • Overvoltage field
  • Over field flow
  • Increase / decrease the generator voltage
  • Disconnect voltage measurement
  • Cut off the field
  • Increasing the field temperature
  • Deviation of the Volts / HZ ratio
  • Frequency reduction
  • 6 Input contacts – programmable by the operator
  • 4 Output contacts – programmable by the operator
  • Independent display of voltage and excitation current scorpions
  • RS-485 communication port and Ethernet
  • Datalogger created to record errors and events

The power converter used is a three-phase rectifier bridge thyristor type. The selected configuration is a three-thyristor half-wave rectifier bridge or a six-thyristor full-wave rectifier bridge.

The six-thyristor rectifier bridge can be used to apply positive and negative voltage to the generator field for two-way voltage to the field.

Both three-thyristor and six-thyristor bridges include heatsinks, cooling fans, and power semiconductor components.

Ultra-fast fuses in each branch, fuse burning displays, RC network for filtering spock current conduction busbars, protection thermoswitches, thyristor temperature thermometers and pulse isolating transformers are all components that make up the power rectifier bridge section. 

In order to accurately control and monitor the performance of the system, it is necessary to know the current status of the system. A series of variables of generator output and excitation coil should be measured and another series should be calculated using the measured variables.

Excitation current, excitation voltage, generator output voltage, generator current, mains voltage, generator power factor, generator reactive power, active generator power, generator output power, generator output frequency, battery voltage, thyristor temperature are directly measured parameters. The inside of the generator and the temperature of the excitation coil are other required information that can be obtained computationally.

This section is responsible for producing fire pulses of rectifier bridge thyristors. This board is designed for six thyristor rectifier bridges with high thyristor gate current. The required angle of fire is applied to the input of this unit by the standard analog signal 4-20mA or 0-10Vdc and based on the level of analog signal and three-phase sampling of the main voltage lines of the pulses at the desired angles, six thyristor poles are applied. . The pulses applied in this system are of 12 pulses type to increase the assurance of the operation of thyristors.

In the thyristor of this system, the desired load line is to turn on the 20V / 20Ohm thyristor. That is, in the case of no load, the voltage is 20 volts and in the case of short circuit, it gives 1 amp. In order for the di / dt of the thyristor to be less than the allowable value, the load line of the thyristor gate driver must be below this load line. The flow diagram of the thyristor gate driver is as follows.

SECON-2000 excitation system is designed for local and remote control, which includes the following components:

  • Push Buttons and Switches
  • Lamp test, Reset, Acknowledge keys for alarm alarm
  • Switches: Auto / Manual Mode
  • AVR Raise / lower (with Center Position)
  • Touch Screen
  • Optionally the system can have a touch screen. In this case, in addition to the instantaneous values of the electrical parameters, the status of system errors can also be viewed by this screen, which can be selected locally or remotely.
  • Alarm Annunciator
  • With a 20 window announcer, you can see the errors in the system and the status of some equipment, such as the circuit break key.
  • This alarm alarm is controlled directly via SECON-Digital.

A large power transformer that is parallel to the generator output is usually used to power the excitation system. This transformer is designed according to the generator terminal voltage and compatible with the needs of the generator field. The transformer provides the full load of the generator excitation and a safety margin value is considered for possible overloads. The power (KVA) and secondary voltage of the transformer will be the maximum amount of power that can be delivered to the field under full load conditions.

A power supply transformer can be replaced by other AC sources between frequencies (50-400Hz) such as PMG or auxiliary windings if they can provide the required power. The power transformer intended for SECON-2000 excitation system is Cast resin with Aluminum Foil, which can be selected according to the customer’s order of dry or oily cold air.

PPT transformer can be provided with safety protection, in which case the protection will be of metal type with mesh and one-piece roof with opening doors and IP21 degree of protection. The color of the body is caterpillar yellow with initial stainless steel coating, which can be changed according to the customer’s order. PPT transformers have overheat protection as standard and can include HV / LV fuses and current measuring transformers on request.

Basically, an initial voltage generating circuit may be required at the start of the excitation supply (Shunt, PMG or Aux winding). Especially when the excitation power is supplied by PPT transformer connected to the output of the generator stator winding (Shunt Connected). In this case, the initial voltage generated by the rotor field residue cannot be high enough to start the system.

This external source can be supplied from an AC voltage (an external auxiliary transformer) or a DC voltage (from the home battery power supply). When Field Flashing is required we will need a Field Flashing circuit and an application circuit to the field circuit. Applying this initial current will allow the thyristors to conduct and increase the power of the system.

A series-positive diode also prevents the battery from reversing current through the rectifier bridge to the batteries. Usually the battery voltage is 125Vdc, but the system designed for this section also allows the use of batteries with 220Vdc voltage.

The technology used in this section is IGBT type power switches that provide the initial starting power in the form of soft start and in the field of field current control.

The excitation system must withstand the faults and abnormal conditions of the system caused by the transient conditions for the generator winding. This situation occurs when the main circuit is shorted (Faults) and the generator goes out of circuit or the generator goes out of sync, and at this time there is an unwanted excitation to deliver several megawatts of power to the power section. In this case, the extra energies of the system cause high voltages in the system and this energy must be controlled by various embedded circuits.

The protection systems installed for this section include the following.

  •  Metal Oxide Varistor
  • DC Field Breaker
  • Field Discharge
  • Free Wheel Diode
  • Crow Bar Circuit

The two current protections to consider are high current protection and high voltage protection. It must also be specified which of these protections can give the DC contactor a trip output. This trip also causes the main circuit breaker of the generator to be disconnected. Of course, it is possible that a series of these protections are present in the old system and remain in the circuit.

High current protection

With a Circuit Breaker at the three-phase input of the rectifier bridge, there is no need for a separate high current protection relay.

Improper fuzzy sequence protection

The order of the phases connected to the system must be clockwise. Therefore, it is necessary to place in one part of the protection circuit system against incorrect fuzzy arrangement.

Reactive power consumption protection

Under no circumstances should the generator consume reactive power. The state in which the generator consumes reactive power is called Under Excitation. The detection of this case is done by SECON-Digital and in case of such a situation, it can be fixed if it can be fixed, otherwise the cut-off command will be issued to the main output contactor.

V / F protection

This value represents the amount of generator flux. In fact, the value of V / F should be limited. This is the responsibility of SECON-Digital. In this case, SECON-Digital must change the amount of excitation current so that it does not exceed the allowable value.

Rotor thermal protector

The temperature of the rotor winding is measured by the central controller by measuring its ohm value at any time. If it exceeds a certain value, the alarm is issued first, and if it exceeds the allowable limit, the cut-off command is issued to the main output contactor.

How to measure the rotor temperature is given in the section on measuring systems.

Thermal protection of thyristors

The heatsink temperature of thyristors is measured by a central controller. In case of exceeding a certain limit, an alarm is issued and if it exceeds the allowable value, the cut-off command is issued to the main output contactor.

Short circuit protection

If the output of the rectifier bridge is shorted, it must be protected against this problem. A short circuit is a situation where the output voltage is low but the output current is high. This protection is done by the central controller. A short circuit is considered when the voltage is below the limit and the current is above the limit. In other words, if the voltage to current ratio (output resistance) is less than a certain limit, a short circuit is considered.

It is designed and implemented on a computer to make settings as well as view a series of values. This software connects to SECON-Digital via Ethernet port. All settings can be done only by computer. In this connection, the computer is selected as the Master and SECON-Digital as the Slave. The capabilities that this software provides are as follows:

Adjust various system parameters

When the user enters the settings page, he can adjust the system parameters. Login to this page requires a password with the required access level. Some of these parameters are:

Temperature and Warning Time of the rotor winding
Temperature and time Shut down the rotor winding
Temperature and time of Warning heatsink thyristors
Temperature and time Shut down thyristors
PID controller coefficients
High limit and Warning time for battery voltage
Low limit and Warning time for battery voltage
Generator start time
Delays required in the program
High limit of excitation coil voltage
High limit of excitation coil current
Generator reactive power limit
High limit of generator power factor
View input and calculated variables

Analog input value All system inputs can be viewed by the system software. Some of these inputs are:

Excitation current and voltage
Rotor winding temperature
Mains voltage
Wattage and current of the generator
Generator power factor, frequency and speed
Active and reactive power of the generator
Apparent power of the generator
Heat sink temperature of thyristors (6 thyristors)
Battery voltage (control)
Device operating hours
Number of times the main contactors and switches are switched on and off
Draw graphs of different variables

For a more detailed study of system performance, changes in system variables can be viewed as curves on the computer. Some of these parameters are:

Stimulation flow
Generator voltage and current
Generator power factor
Generator reactor power
Active power of the generator
Apparent power of the generator
View the status of digital signals

The status of all digital signals can be viewed by the software. These signals are:

The main output contactor is open or closed
Open or close the main generator output contactor
SECON-Digital in Run or Stop mode
All digital outputs from SECON-Digital
All digital inputs from SECON-Digital
All Warning
All Shutdowns

Knowledge-based company of Hoorpendar, as the first designer and manufacturer of static excitation system of power plant generator, is ready to design, produce and provide the services required by its customers in the field of generator excitation system. SECON-2000 series excitation system includes static excitation systems up to 2000A flow power individually or with plugs.

  • PLC-based digital controller
  • Voltage regulation with accuracy ± 0.5%
  • Fast performance response
  • Multiple excitation limiter to keep the machine in the allowable operating range
  • Six thyristor rectifier bridge 12 full pulse
  • Input contactor or Circuit Breaker switch (optional motor) in the input power supply
  • Crowbar & Field Discharge
  • DC field switch (optional)
  • Field Flashing control circuit and driver using IGBT technology
  • High power indoor air supply system
  • LCD screen with touch screen to display values and control locally or remotely
  • Digital communication with modern facilities
  • Overload bearing capacity for a short time
  • Overvoltage protection of the field
  • Reliable stability in operation with the network or other machines
  • Generating thyristor trigger pulses even in the event of possible errors
  • Provide excitation current up to 2000A
  • Ability to create Redundancy for control and thyristor bridges
  • Compatible with most power plant control systems
  • Ability to detect and view errors remotely

Voltage Regulation

SECON-Digital regulates the RMS voltage of the generator from idle to full load with an accuracy of ± 0.5%, digital signal processing and efficient regulation algorithms are the result of the experience and expertise of Horpandar in designing and implementing control systems using hardware Advanced Schneider France has provided a reliable and stable system.

 

Out put

SECON-Digital provides an isolated 4-20mA or 0-10Vdc isolated analog output signal for the power supply angle control circuit. The DC current generated by the power supply provides current to the generator field or excitation. SECON-Digital can actually support any other rectifier bridge that can be controlled by this analog signal, which can make the system efficient for many motors or synchronous generators with faulty controllers.

 

Stability

SECON-Digital uses a stable PID controller (Proportional, Integral, Derivative). SECON-Digital has a stable initial programmable setting (PID). Therefore, a stable standard setting is considered for most machines. In addition, in SECON-Digital it is possible to adjust the parameters more precisely with a group of other settings according to each generator to optimize the performance of the system. The settings software includes a PID selection program that helps select the correct PID.

 

SECON-Digital also includes minimum and maximum excitation limits, VAR / PF controllers and stator current limiters to optimize stability and performance in transient conditions with additional stability parameters.

 

PID settings (PID)

SECON-Digital has made it possible to reset the PID parameters precisely to optimize system stability for different machines. The software is smart in this area and prevents numbers from entering outside the allowed range.

Under frequency limiter or V to Hz ratio (Under frequency limiter or V / Hz Ratio limiter)

SECON-Digital offers the customer two choices: sub-frequency limiter or V / Hz ratio limiter. This limit prevents the generator from overflowing.

 

Soft-Start Voltage build-up

SECON-Digital has a soft voltage driver whose parameters can be adjusted by the user. This soft starter controls the allowable rate of increase of the generator voltage and prevents over-jump of the voltage during the start of the generator. Soft startup is enabled in both AVR and FCR modes.

 

Set point Control

SECON-Digital allows the work point to be set externally and remotely in addition to the local panel. The operating mode operating point can be adjusted from Raise / Lower contacts or analog input signal 4-20mA or ± 10Vdc. These settings are also available through communication ports according to the Modbus protocol.

Field Current Regulation operating Mode

SECON-Digital provides a manual operation channel called field flow regulation mode (FCR). In this mode, SECON-Digital regulates the output current of the power bridge. This mode is not dependent on the generator voltage measurement input and therefore provides a backup to control the excitation when the voltage input is lost. In FCR mode, the operator must manually adjust the excitation current to reach the rated voltage based on load changes.

 

VAR or PF control function mode
(VAR / Power Factor Controller Operating Mode)

SECON-digital also has two additional control modes for using the generator when connected to the global network. In VAR control mode, SECON-Digital can regulate the amount of reactive power output of the generator to the set value required by the operator, or in PF mode can control the amount of reactive power output of the generator according to changes in active power to the required power factor. To regulate.

Over-Excitation Limiters

Superstimulation limiters monitor the field output current from the voltage regulator or static excitation and limit the field current to prevent the field temperature from rising.

The Over-Excitation Limiter (OEL) function includes a temperature-reducing property to prevent damage to the rotor due to the application of successive forces.

OEL is active in all modes except FCR mode. In FCR mode, the function of this limiter is optional.

SECON-digital offers two types of super-excitation limiters to choose from. Summing point and takeout methods.

 

Summing Point Type OEL

In this method, three levels of high-medium-low OEL current are defined for on-line operation. The generator can operate continuously at low-current OEL level and for scheduled times at medium-high OEL and high-OEL levels. Two levels of high and low OEL current are defined for off-line operation (main key open). The generator can operate continuously at low OEL current level and for programmed time at high OEL current level.

 

Take Over Type OEL

The Over-excitation limiter of the Take Over method determines a field current level whose range is in an inverse time profile. Two adjustments of flow levels and time components are defined for the Take Over method.

Separate curves may be selected for On-line and Off-line operation. If the system enters the above excitation conditions, the excitation current is limited by following a selected curve. The selection of on-line and off-line surfaces and curves is achieved by a selective OEL.

 

Minimum Excitation on Limiter

The minimum excitation limiter prevents the reduction of the generator field current below the safe operating level. This restriction prevents the poles from slipping and damaging the machine. This also limits the amount of reactive power absorbed by the machine based on the operator’s defined settings. A minimum excitation limiting curve (UEL) based on an allowable reactive power level at zero active power can be used for this purpose.

The UEL limiting function is optional in FCR mode.

Stator Current Limiter

Stator current limiter (SCL) measures the stator current and prevents the stator temperature from rising. The SCL limiter operates in all modes except the FCR mode.

In FCR mode, the controller announces the stator overcurrent conditions, but the limiter is off. There are two levels of SCL flow: high and low. The generator can operate continuously at the SCL current level but only at the scheduled SCL current level for a long time.

 

Auto tracking between operating modes

SECON-Digital is a smart device that can automatically change the setting point by changing the control modes. This operation allows the operator to change the control mode during operation without causing a bump (Lump) so as not to disturb the power system.

Replacement of old controllers with modern digital system of static excitation SECON-2000 with design according to customer order

A number of power plants in the country have outdated equipment, with high repair costs and the impossibility of providing spare parts. DC cut-off switches, motorized rheostats, faulty rotating actuators, damaged commutators, wear and tear of various components in voltage regulators are just some of the problems of the country’s old power plants, which results in increased overhead costs and increased generator downtime.

Replacing compound rotating stimuli or SCT / PPT controls with a SECON-2000 series excitation system is a viable solution to these problems.

SECON-2000 digital static excitation with flexible design has made it possible to update the old systems of the country’s power plants with economic justification and can be used for most small and large power plants in the country.

  • The coil of the swivel excitation system is short-circuited or partially discharged.
  • To increase the range of the generator, you need to increase the excitation current.
  • Increased repairs and downtime have reduced system reliability.
  • The carbon dust from the commutator brush reduces the insulation and raises the temperature.
  • Due to the carbon dust in the commutator, problems such as spark or reduced insulation have been created.
  • Your generator commutator is worn out and needs to be replaced.
  • The vacuum cleaners of the commutators need to be repaired regularly and their overhaul is also difficult.
  • It is not possible to supply spare parts for existing electromechanical equipment.
  • The DC field disconnect switch is difficult to operate and its replacement is very costly and time consuming.
  • You need an automated excitation system in your control unit for automatic start-up or automatic synchronization.
  • You need a system with fast voltage compensation to match the new relays and prevent unwanted trips.
  • You want to increase your performance efficiency by increasing the unit output excitation consumption by reducing it.
  • You do not have enough repairmen to repair electromechanical and rotating parts.
  • You need the ability to record information, and this feature is present in digital excitation systems.

The basic principles of a static excitation regulator are continuous measurement of voltage and current and comparison with adjustment points and application of new voltage suitable for excitation. Increases the field current when the excitation system senses a decrease in generator voltage, and decreases the excitation current when it senses an increase in generator voltage. In this case, DC static excitation is applied directly to the field through the Slip Ring.

A normally designed static excitation system may have several different parts, but there are always six basic components at the core of the system.

The main components are:

  • Digital AVR
  • Power Electronics Thyristor Bridge))
  • Measuring Instrument)
  • SCR Firing Unit))
  • Touch Screen HMI and Switches
  • Main power supply Shunt Transformer or PMG))In the custom design of the excitation system, various capabilities and facilities can be selected for your application. Suggested features include: 
  • Redundancy of the Power Electronics))
  • Redundancy of the Control Electronics)
  • Several digital connections to different protocols
  • Digital generator protection relays
  • Remote control and integration with DCS control system and turbine control panel
  • Field Flashing system
  • Fast De-excitation system
  • Automatic synchronizer
  • Coordinate with available space and boards

The heart of the SECON-2000 excitation system is its digital controller. This section has been selected by a programmable controller (PLC) from Schneider Premium Series. This PLC, which is of industrial type, receives the values of different parameters that are read by the measuring equipment and is in the standard range of voltage or current through its analog input cards and the status and error signals of the system through its digital input cards. After analysis and processing in its powerful processor section, it applies digital commands through the digital output card and the amount of voltage required for the rectifier bridge in the form of analog values through the analog output card.

The digital controller, while providing the analog signal of the fire pulse section and controlling the DC voltage of the thyristor bridge rectifier output, continuously monitors the complete system to control, apply the limitations and the operation of the synchronous machine within its tolerable range.

Real Time monitoring for testing and analysis, graphical display of parameters, display of digital input and output statuses are other features of this section that can be accessed by software provided for PC.

The specifications of this section are as follows:

PLC based design
It has four control modes with the ability to change the working mode without creating a shock
Automatic Voltage Regulation (AVR)
Field Current Regulation (FCR)
Power Factor Regulation (PFR)
Var control
0.5% accuracy of voltage regulation
Two programmable analog outputs for the analog display
Perform settings by computer software or HMI
PID controller
Line voltage drop compensator
Soft voltage starter made initially
Flexible remote control points
Implemented limiting functions
Above stimulation limiter
Restrictor following stimulation
Volts / HZ ratio limiter or frequency reduction limiter
Stator current limiter

Input contact

Relative analog voltage or current
Digital communication
Implemented protection functions
Overvoltage field
Over field flow
Increase / decrease the generator voltage
Disconnect voltage measurement
Cut off the field
Increasing the field temperature
Deviation of the Volts / HZ ratio
Frequency reduction
6 Input contacts – programmable by the operator
4 output contacts – programmable by the operator
Independent display of voltage and excitation current scorpions
RS-485 communication port and Ethernet

Datalogger created to record errors and events

The power converter used is a three-phase rectifier bridge thyristor type. The selected configuration is a three-thyristor half-wave rectifier bridge or a six-thyristor full-wave rectifier bridge.

The six-thyristor rectifier bridge can be used to apply both positive and negative voltage to the generator field for two-way voltage to the field.

Both three-thyristor and six-thyristor bridges include heatsinks, cooling fans, and power semiconductor components.

Ultra-fast fuses in each branch, fuse burning displays, RC network for filtering spock current conduction bushes, protection thermoswitches, thyristor temperature thermometers and pulse isolating transformers are all components that make up the power rectifier bridge section. 

In order to accurately control and monitor the performance of the system, it is necessary to know the current status of the system. A series of variables of generator output and excitation coil should be measured and another series should be calculated using the measured variables.

Excitation current, excitation voltage, generator output voltage, generator current, mains voltage, generator power factor, generator reactive power, active generator power, generator output power, generator output frequency, battery voltage, thyristor temperature are directly measured parameters. Inside the generator and the temperature of the excitation coil are other required information that can be obtained computationally.

This department is responsible for producing fire pulses of rectifier bridge thyristors. This board is designed for six thyristor rectifier bridges with high thyristor gate current. The required angle of fire is applied to the input of this unit by the standard analog signal 4-20mA or 0-10Vdc and based on the level of analog signal and three-phase sampling of the main voltage lines of the pulses at the desired angles, six thyristor poles are applied. . The pulses applied in this system are of 12 pulses type to increase the assurance of the operation of thyristors.

In the thyristor of this system, the desired load line is to turn on the 20V / 20Ohm thyristor. That is, it gives a voltage of 20 volts in idle mode and 1 amp in short circuit mode. In order for the di / dt of the thyristor to be less than the allowable value, the load line of the thyristor gate driver must be below this load line. The flow diagram of the thyristor gate driver is as follows.

SECON-2000 excitation system is designed for local and remote control, which includes the following components:

Push Buttons and Switches
Lamp test, Reset, Acknowledge keys for alarm alarm
Switches: Auto / Manual Mode
AVR Raise / lower (with Center Position)
Touch Screen

Optionally the system can have a touch screen. In this case, in addition to the instantaneous values of the electrical parameters, the status of system errors can also be viewed by this screen, which can be selected locally or remotely.

Alarm Annunciator

With a 20-window announcer, you can see the errors in the system and the status of some equipment, such as the circuit break key.

This alarm alarm is controlled directly via SECON-Digital.

A large power transformer that is parallel to the generator output is usually used to power the excitation system. This transformer is designed according to the generator terminal voltage and compatible with the needs of the generator field. The transformer provides the full load of the generator excitation and a safety margin value is considered for possible overloads. The power (KVA) and secondary voltage of the transformer will be the maximum amount of power that can be delivered to the field under full load conditions.

A power supply transformer can be replaced by other AC sources between frequencies (50-400Hz) such as PMG or auxiliary windings if they can provide the required power. The power transformer intended for the SECON-2000 excitation system is Cast resin with Aluminum Foil, which can be selected according to the customer’s order, such as dry, cool or oily air.

PPT transformer can be provided with safety protection, in which case the protection will be of metal type with mesh and one-piece roof with opening doors and IP21 degree of protection. The color of the body is caterpillar yellow with initial stainless steel coating, which can be changed according to the customer’s order. PPT transformers have overheat protection as standard and can include HV / LV fuses and current measuring transformers on request.

Basically, an initial voltage generating circuit may be required at the start of the excitation supply (Shunt, PMG or Aux winding). Especially when the excitation power is supplied by PPT transformer connected to the output of the generator stator winding (Shunt Connected). In this case, the initial voltage generated by the rotor field lag cannot be high enough to start the system.

This external source can be supplied from an AC voltage (an external auxiliary transformer) or a DC voltage (from the home battery power supply). When Field Flashing is required we will need a Field Flashing circuit and an application circuit to the field circuit. Applying this initial current will allow the thyristors to conduct and increase the power of the system.

A positive-pole series diode also prevents the reverse current from flowing through the rectifier bridge to the batteries. Usually the battery voltage is 125Vdc, but the system designed for this section also allows the use of batteries with 220Vdc voltage.

The technology used in this section is IGBT type power switches that provide the initial starting power in the form of soft start and in the field of field current control.

The excitation system must withstand the faults and abnormal conditions of the system caused by the transient conditions for the generator winding. This situation occurs when the main circuit is shorted (Faults) and the generator goes out of circuit or the generator goes out of sync, and at this time there is an unwanted excitation to deliver several megawatts of power to the power section. In this case, the extra energies of the system cause high voltages in the system and this energy must be controlled by various embedded circuits.

The protection systems installed for this section include the following.

  • Metal Oxide Varistor
  • DC Field Breaker
  • Field Discharge
  • Free Wheel Diode
  • Crow Bar Circuit

The two current protections to consider are high current protection and high voltage protection. It must also be specified which of these protections can give the DC contactor a trip output. This trip also causes the main circuit breaker of the generator to be disconnected. Of course, it is possible that a series of these protections are present in the old system and remain in the circuit.

 

High current protection

With a Circuit Breaker at the three-phase input of the rectifier bridge, there is no need for a separate high current protection relay.

 

Improper fuzzy sequence protection

The order of the phases connected to the system must be clockwise. Therefore, it is necessary to place in one part of the protection circuit system against incorrect fuzzy arrangement.

 

Reactive power consumption protection

Under no circumstances should the generator consume reactive power. The state in which the generator consumes reactive power is called Under Excitation. The detection of this case is done by SECON-Digital and in case of such a situation, it can be fixed if it can be fixed, otherwise the cut-off command will be issued to the main output contactor.

 

V / F protection

This value represents the amount of generator flux. In fact, the value of V / F should be limited. It is the responsibility of SECON-Digital to limit this. In this case, SECON-Digital must change the amount of excitation current so that it does not exceed the allowable value.

 

Rotor thermal protector

The temperature of the rotor winding is measured by the central controller by measuring its ohm value at any time. If it exceeds a certain value, the alarm is issued first, and if it exceeds the allowable limit, the cut-off command is issued to the main output contactor.

How to measure the rotor temperature is given in the section on measuring systems.

 

Thermal protection of thyristors

The heatsink temperature of thyristors is measured by a central controller. In case of exceeding a certain limit, an alarm is issued and if it exceeds the allowable value, the cut-off command is issued to the main output contactor.

 

Short circuit protection

If the output of the rectifier bridge is shorted, it must be protected against this problem. A short circuit is a situation where the output voltage is low but the output current is high. This protection is done by the central controller. A short circuit is considered when the voltage is below the limit and the current is above the limit. In other words, if the voltage to current ratio (output resistance) is less than a certain limit, a short circuit is considered.

Designed and implemented on a computer to make settings as well as view a series of values. This software connects to SECON-Digital via Ethernet port. All settings can be done only by computer. In this connection, the computer is selected as the Master and SECON-Digital as the Slave. The capabilities that this software provides are as follows:

Adjust various system parameters

When the user enters the settings page, he can adjust the system parameters. Login to this page requires a password with the required access level. Some of these parameters are:

Temperature and Warning Time of the rotor winding
Temperature and time Shut down the rotor winding
Warning temperature and time of thyristors
Temperature and time Shut down thyristors
PID controller coefficients
High limit and Warning time for battery voltage
Low limit and Warning time for battery voltage
Generator start time
Delays required in the program
High limit of excitation coil voltage
High limit of excitation coil current
Generator reactive power limit
High limit of generator power factor
View input and calculated variables

Analog input value All system inputs can be viewed by the system software. Some of these inputs are:

Excitation current and voltage
Rotor winding temperature
Network voltage
Wattage and current of the generator
Generator power factor, frequency and speed
Active and reactive power of the generator
Apparent power of the generator
Heat sink temperature of thyristors (6 thyristors)
Battery voltage (control)
Device operating hours
Number of times the main contactors and switches are disconnected and reconnected
Draw graphs of different variables

For a more detailed study of system performance, changes in system variables can be viewed as curves on the computer. Some of these parameters are:

Stimulation flow
Generator voltage and current
Generator power factor
Generator reactor power
Active power of the generator
Apparent power of the generator
View the status of digital signals

The status of all digital signals can be viewed by the software. These signals are:

The main output contactor is open or closed
Open or close the main generator output contactor
SECON-Digital in Run or Stop mode
All digital outputs from SECON-Digital
All digital inputs from SECON-Digital
All Warning
All Shutdowns